Fair use allows copyrighted works to be used without permission in instances of "public interest" -- that is, in research, teaching, criticism, commentary, satire, news reporting and library archiving. Now, this does not mean that you can use an entire work and claim fair use. There are guidelines to follow:
How the work is being used -- Are you using the work for commercial or educational purposes? Are you turning the assignment in to just the teacher or are you distributing the work to the whole class? It should be obvious that using an image for commercial use or to distribute does not count as fair use.
Nature of the work -- Ideas and facts are public domain. In some cases, public interest and social usefulness will trump copyright.
Amount of the work used -- Are you quoting a passage in an article or using the whole article? Are you using a still from a film or the whole film? While there may be cases where you can safely use an entire piece, the less you use, the more likely it will be considered fair use.
Effect on the original -- Does your use effect the value or demand for the original piece? You can't use a piece in any way that will negatively effect the original work or copyright owner.
As you can see, even with the above guidelines, fair use isn't clear. In most cases, you should be able to use copyrighted images in your assignments as long as you are not publishing or distributing the image, claiming the image as your own, selling the image, or altering the image in a way that lessens the market for the original image. See more below on sharing copyrighted content in your classes.
That said, make sure to credit the original creator and, when possible, contact them to get permission. Neither I nor the library can be responsible if you infringe on copyright.
Under certain conditions specified in the law, libraries and educators are allowed to provide their students photocopies and other reproductions. One of these specified conditions is that the reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user uses the copyright materials in excess of "Fair Use" guidelines, that user may be liable for copyright infringement.
While there are no perfect guidelines for fair use in the classroom, here's some tips to help make sure both faculty and students are in compliance: